1. Field of the Invention
The present invention combines the field of surface mount technology with the field of flexible circuit technology.
2. The Prior Art
A flexible circuit is a multiplanar interconnection system having a flexibility which permits the circuit board to be bent, folded and/or rolled into a desired shape. Such flexibility eliminates many connectors, wires and cables which would otherwise be necessary in connection with the use of a corresponding hardboard or ceramic type circuit. Elimination of connections conventionally required for hardboard circuitry increases reliability, reduces costs, simplifies automation and increases circuit density and performance. While more expensive per unit area than hardboard, flexible circuitry achieves a savings when used as a replacement for two hardboard elements with connectors.
However, utilization of flexible circuit technology has been limited by problems with regard to dimensional stability and the integrity of adhesive bonds between adhering laminae, especially at high temperature.
In standard leaded circuit board connections, holes are drilled through the circuit board and the leads of the device to be mounted thereon, e.g. resistor, capacitor, IC's are inserted and soldered into the holes. The earliest "boards" for integrated circuits were ceramic. The difficulty of generating holes and achieving plating through those holes demanded a different type of mounting technology for such circuit boards. Surface mount technology offers a route around the problem of drilling and finishing holes for reception of component leads. Further, surface mount technology lends itself better to smaller component size, provides higher circuit density, especially in view of the fact that it permits both sides of the circuit board to be completely used. The major existent problem with surface mount technology resides in thermal expansion mismatches between the mounted devise and the substrate or circuit board on which the devise is mounted. Differentials in thermal expansion as between the device and the substrate result in solder joint cracking and the breaking of electrical and physical connections between the mounted component and the circuit board substrate.